A fire set by an employee at Chicago's main air traffic control center led to the cancellation of nearly 1,800 flights at the city's two major airports on Friday, snarling air traffic across the nation and the globe.

Flights resumed after a delay of about four hours, but there were major bottlenecks across the air system.

The blaze at the facility in Aurora, about 40 miles outside of downtown Chicago, was reportedly set by a 36-year-old contract worker who was angry at being transferred to Hawaii and wanted to sabotage the telecommunications center, which coordinates high-altitude flights coming in and out of Chicago's O'Hare and Midway airports.

The incident caused major delays at O'Hare International, one of the world's busiest, and the domestic hub Midway International Airport, affecting flights from almost every state and routes with Europe, Asia and Latin America.

Local broadcaster WGN reported law enforcement officials as saying the male employee cut himself while trying to sever wires at the center before dousing the lines in gasoline and setting them on fire.

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Chaos: All flights into and out of Chicago's O'Hare and Midway international airports were grounded early on Friday - along with any scheduled to cross the Midwest - after a fire broke out in the basement of the Chicago Air Route Traffic Control Center in Aurora, about 40 miles west of downtown Chicago

Emergency: Authorities found a male contract employee of the FAA in the basement telecommunications room of the Aurora facility, suffering self-inflicted wounds believed to have been caused when he cut crucial air traffic wires

Stranded: Thousands of travelers - both in Chicago and across the country - have been affected by the incident, which saw at least 800 flights cancelled

Mecca: The air traffic control center in Aurora is a major communications hub for Chicago O'Hare and Midway airports, causing major delays. It handles the high altitude aircraft coming in and out of both airports

Full up: Chicago O'Hare - America's second-busiest airport - is seen stacked full of planes on Friday morning following a major ground stop that has affected thousands across the country

WHAT DOES IT MEAN FOR FRIDAY TRAVELERS?

Flights resumed at a 'reduced rate' from noon after extensive ground stop

Southwest suspended all flights out of Midway airport until at least noon

Flights to Chicago were diverted to other airports

The building was evacuated as the fire broke out about 5.40am but emergency crews were able to extinguish the blaze.

The employee was found wounded in the basement telecommunications area but was alive.

He was taken to hospital along with another man, who suffered smoke inhalation.

There were 1,473 flights into and out of the two airports that were canceled by 12.22 pm CDT (1722 GMT), according to tracking website flightaware.com, leaving thousands of travelers stranded.

Later in the day ABC News reported the disruption had increased to1,800 flights.

'There's cascading delays because nothing can take off bound for Chicago from anywhere,' said Doug Church, spokesman for the National Air Traffic Controllers Association, a union of air traffic controllers.

'The impact is national and major.'

At O'Hare, passengers were scrambling to find alternative transportation or bracing for long delays.

'I'm shocked at how calm everyone is. With everything going on in the world, maybe we're all managing our expectations. It's a fire in Aurora, it's not ISIS,' said Cynthia Stemler of the Chicago suburb of Lake Bluff, who was heading to Newark, New Jersey, in a reference to the militant Islamic group at war in Syria and Iraq.

O'Hare is the nation's second-busiest airport.

It is the main hub for United Airlines and a major hub for American Airlines.

From January to August, more than 580,000 flights departed or landed at O'Hare, the city of Chicago said, citing Federal Aviation Administration data.

Southwest Airlines Co - which operates the majority of flights at Chicago Midway - suspended all flights until noon at Midway and at Milwaukee's General Mitchell International Airport, the airline said in a statement.

Passengers booked on flights that were cancelled will be put rescheduled.

However major delays are expected as the airlines struggle to deal with the overflow.

Flight experts say the main problem affecting flights outside of Chicago is mostly concerned with crew members, who are stuck in Chicago but are likely booked for flights in connecting airports.

Empty: This screen shot provided by FlightAware shows airline traffic at 10:20 a.m. EDT over the United States after hundreds of flights were canceled at Chicago two airports on Friday

Stuck: Passengers are seen waiting at O'Hare International Airport in Chicago, Illinois, one of the world's busiest

Ground stop: At least 800 flights had to be cancelled Friday morning, with the affects rippling across the national air traffic network

Upset: Kanna Ortiz 4, waits in a line after her flight back home to New Jersey was delayed at O'Hare International Airport in Chicago, Friday, September 26, 2014

Empty: Skies above the Chicago area were virtually empty Friday morning, due to a major ground stop at O'Hare and Midway airports because of a fire at an FAA radar facility

Grounded: Southwest Airlines Co - which operates the majority of flights at Chicago Midway - suspended all flights until at least noon

Paralyzed: The skies around Chicago (center) were empty Friday morning after 300 flights were cancelled to and from O'Hare and Midway Airports

According to CBS, the FAA's Indianapolis Center are attempting to fill the gap left by the evacuated Aurora facility

'They are doing what they can to support,' a NATCA official told CBS.

'They have one route for Chicago-area arrivals currently in operation, and are considering ways to add a second.

'They've also developed a non-radar departure route for southbound departures out of the Chicago area.

'Additionally,
they are preparing to handle an increased load of East Coast traffic.
In short, they're doing everything they can to assist.'

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However
the contractor is said to have known exactly what to do to cause the
most damage, and managed to destroy many crucial operational systems,
CBS reported.

The
extent of the damage, coupled with the fire and effects of the water
from the sprinklers, could mean the facility will be down for days.

The
result would mean only a fraction of the traffic that normally operates
at O'Hare and Midway will be able to get in and out of Chicago.

Press conference: Aurora Chief of Police Gregory Thomas (R) and Tom Ahern of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) hold a briefing across from the U.S. Department of Transportation Federal Aviation Administration in Aurora, Illinois

Investigation: Police and FBI inspect a GMC vehicle in the parking lot of the Chicago Air Route Traffic Control Center in Aurora, Ill., believed to be owned by the man allegedly involved with the fire

Long waits: An American Airlines passenger stands in a line with other passengers to rebook their canceled flights after a small fire at the Air Route Traffic Control Center in Aurora disrupted air service though out the region

It
was the second time since May that a problem at one of the Chicago
area's major control facilities prompted a ground stop at O'Hare and
Midway international airports.

In May, an electrical problem forced the evacuation of a regional radar facility in suburban Elgin. A bathroom exhaust fan overheated and melted insulation on some wires, sending smoke through the facility's ventilation system and into the control room.

That site was evacuated for three hours, and more than 1,100 flights were canceled.

The Aurora facility is known as an en-route center, and handles aircraft flying at high altitudes, including those on approach or leaving Chicago's airports.

Air traffic closer to the airports is handled by a different facility and by the control towers located at the airfields.

A computer glitch at a similar facility on the West Coast in April forced a 45-minute shutdown at Los Angeles International Airport.